The present invention concerns a gripper element for a punch or a die of a punching machine. In particular, the invention concerns a gripper element for an arm of a changeover device of a turret punching machine.
Different kinds of turret punching machines are known, provided with a device for exchanging the punch and die pair between the turrets and a magazine of such pairs. In one known machine, each end of the changeover arm has a gripper element formed from two leaf springs, each having a rib for snap-engaging a channel extending from the punch or the die.
This gripper element has the disadvantage of requiring a pair of pneumatic pistons, one for removing the punch or die from the leaf springs, and the other for removing them from their seat and re-engaging them with the leaf springs. Furthermore, the elastic thrust of the leaf springs does not allow the punch or die to be rigidly secured to the gripper element. Finally, this gripper element does not exhibit any angular reference for holding the punch or die.
In another known machine, the gripper element is operated by an axial pneumatic cylinder and comprises two rigid jaws pivoted to the rod of the pneumatic piston. The two jaws are rotated in a mutually opposite direction by means of a fixed cam profile, and are adapted to engage two diametrically-opposed cavities located outside the punch or in an axial hole of the die.
This gripper element has the disadvantage of requiring two different types of jaws for the punch and the die. Furthermore, the connection between two diametrically-opposed cavities does not ensure such a reference as to connect the jaws firmly to the punch or the die during the movement of the changeover arm.